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Improve error message for printf-style format strings - #89340
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…nkov Improve error message for `printf`-style format strings Fixesrust-lang#89173. The following is actually supported today: ```rust fn main() { let num = 5; let width = 20; print!("%*2$x", num, width); } ``` ``` error: multiple unused formatting arguments --> src/main.rs:4:21 | 4 | print!("%*2$x", num, width); | ------- ^^^ ^^^^^ argument never used | || | | || argument never used | |help: format specifiers use curly braces: `{:1$x}` | multiple missing formatting specifiers | = note: printf formatting not supported; see the documentation for `std::fmt` ``` However, as noted in rust-lang#89173, something like ```rust print!("%0*x", width, num); ``` does not give a helpful suggestion. I think this is partly intended, because there actually _is_ no Rust equivalent to this; you always have to use a positional or named argument to specify the width (instead of just using the "next" argument, as `printf` or even `.*` as a precision specifier in Rust would). Therefore, I have added a note: ``` [...] note: format specifiers use curly braces, and you have to use a positional or named parameter for the width --> t2.rs:4:13 | 4 | print!("%0*x", width, num); | ^^^^ = note: printf formatting not supported; see the documentation for `std::fmt` ``` This is not perfect, but it should at least point the user in the right direction, instead of issuing no explanation at all. cc `@lcnr`
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…nkov Improve error message for `printf`-style format strings Fixesrust-lang#89173. The following is actually supported today: ```rust fn main() { let num = 5; let width = 20; print!("%*2$x", num, width); } ``` ``` error: multiple unused formatting arguments --> src/main.rs:4:21 | 4 | print!("%*2$x", num, width); | ------- ^^^ ^^^^^ argument never used | || | | || argument never used | |help: format specifiers use curly braces: `{:1$x}` | multiple missing formatting specifiers | = note: printf formatting not supported; see the documentation for `std::fmt` ``` However, as noted in rust-lang#89173, something like ```rust print!("%0*x", width, num); ``` does not give a helpful suggestion. I think this is partly intended, because there actually _is_ no Rust equivalent to this; you always have to use a positional or named argument to specify the width (instead of just using the "next" argument, as `printf` or even `.*` as a precision specifier in Rust would). Therefore, I have added a note: ``` [...] note: format specifiers use curly braces, and you have to use a positional or named parameter for the width --> t2.rs:4:13 | 4 | print!("%0*x", width, num); | ^^^^ = note: printf formatting not supported; see the documentation for `std::fmt` ``` This is not perfect, but it should at least point the user in the right direction, instead of issuing no explanation at all. cc ``@lcnr``
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…arth Rollup of 6 pull requests Successful merges: - rust-lang#87868 (Added -Z randomize-layout flag) - rust-lang#88820 (Add `pie` as another `relocation-model` value) - rust-lang#89029 (feat(rustc_parse): recover from pre-RFC-2000 const generics syntax) - rust-lang#89322 (Reapply "Remove optimization_fuel_crate from Session") - rust-lang#89340 (Improve error message for `printf`-style format strings) - rust-lang#89415 (Correct caller/callsite confusion in inliner message) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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Fixes#89173. The following is actually supported today:
However, as noted in #89173, something like
does not give a helpful suggestion. I think this is partly intended, because there actually is no Rust equivalent to this; you always have to use a positional or named argument to specify the width (instead of just using the "next" argument, as
printfor even.*as a precision specifier in Rust would). Therefore, I have added a note:This is not perfect, but it should at least point the user in the right direction, instead of issuing no explanation at all.
cc @lcnr